This invention relates to a magnetic tape cassette, and more specifically to a magnetic tape cassette having improved tape guides.
Throughout this specification, the orientation of a conventional magnetic cassette as well as that of the present invention will be named on an assumption that the cassette which comprises a pair of flat half parts is placed horizontally and the side of the cassette where the magnetic tape is exposed will be called the "front portion". Thus, the upper one of the half parts will be called the "upper part" and the lower one of the half parts will be called the "lower part".
A magnetic tape cassette is an enclosure generally comprising a housing which consists of a set of upper and lower half parts, a pair of tape-winding hubs accommodated in the housing, and a length of magnetic tape wound round the hubs so that it can be unwound from one hub and taken up by the other, an vice versa, passing the front portion of the housing. To allow the magnetic tape to run uniformly in close contact with the magnetic head of a recorder, various guide rollers and fixed guide ribs are provided in the front portion of the housing. Of those, fixed tape guides are the subject of improvements in accordance with the present invention.
In FIGS. 1 and 2 are shown conventional fixed tape guide ribs provided in the front portion of a magnetic tape cassette. For the convenience of explanation the upper and lower half parts of the housing are not shown. To guide a magnetic tape properly, the conventional arrangement includes two pairs of guide ribs 3, 4 and 5, 6, protruding frontwardly of the housing, respectively, from recesses 1, 2 which are aligned to reference openings 12, 13 formed in the upper and lower half parts of the housing to control the cassette position relative to the recorder. (Refer to FIG. 5.) These ribs are upright in parallel with the surface of the magnetic tape T, with a height greater than the width of the tape. The plane connecting the ridges (straight front edges) of the guide ribs 3, 4, 5, 6 constitutes a plane that defines a path for the magnetic tape.
In plastic molding of the casing, molten resin is poured into the mold cavity at the gate G until the resin flow comes to an end at the points where guide ribs are to be formed. At the end points the resin frequently is not thoroughly filled up, leaving bubbles in the molded part of causing discoloration (reflecting the reaction of monomer in the resin) due to insufficient degassing. These bubbles, in turn, can impair the outward appearance of the finished article or produce dimensional accuracy falling short of design requirements.
In another example of the prior art, as shown in FIGS. 3 and 4, rings 7, 8 are provided around the upper and lower ends, respectively, of reference openings 1, 2 and are integrally fixed to guide ribs 3, 4 and 5, 6. These rings are primarily intended, after precision finish, for alignment with the corresponding openings of the upper and lower half parts of the housing, to serve as dimensional standards for other components and for the recorder to handle the cassette. In the example being described, too, the front edges of the guide ribs 3, 4, 5, 6 are the points where molten resin finally reaches during the molding. This combines with the relatively narrow width often to interrupt the resin flow and cause inadequate resin flow, again presenting the aforesaid problems typified by malformation (shown exaggerated) along the front edges of the ribs 3, 4, 5, 6 as shown for the rib 4 in FIG. 10.